Recovery of ammonium and sodium sulfates from wash waters



MalCh 20, 1956 K. D. ASHLEY ET AL RECOVERY OF AMMONIUM AND SODIUM SULFATES FROM WASH WATERS 2 Sheets-Sheet l Filed June 25, 1953 @WWE dll

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u@ IME, wow, w #Si 1N VE N TO R5 KENNETH 0.4514096 WML/,4M F.54NBOP/V ATTORNEY l BY @um March 20, 1956 K D ASHLEY ET AL 2,739,044

RECOVERY OF' AMMONIUM AND SODIUM SULFATES FROM WASH WATERS Filed June 25, 1953 2 Sheets-Sheet 2 United RECOVERY or AMMoNIUM AND sonrUM SULFATES -FRM WASH WATERS YIienne'th D. Ashley,-Stam`ford, 'and `Willliam E. Sanborn, Rowayton, Conn., assignors to American Cyanamid Company, -New York, N. Y., a corporation offMaine Application June 52s,' 195s, sensi Nuez/nosa firearms. 4v(ci. 23a-3oz) ammonia are used in the formation of the silica andVIA ialumina gels. During the formation of the gels, fsodium *sulfate and ammoniumsulfate ,are naturally formed and Ltion olfa -portion of the ammonium 'sulfateeout of solution prior 'tto 'any crystallization of the sodium sulfate, Whereby"the ammonium sulfate may be separated van'l collected in relatively pure form. 'The remaining YYsolution'ma'y `then be separated and recycled, .if desired, 'for example, to a'p'oint 'of the'operation` prior tothe separa- 'tion of the double'salts.

in Vthis way, 'relatively pure sodium sulfate, as Well as -elatively pure ammonium sulfate, are recovered from thedilute'aqueo'us wash Water and, at the same time, any lwastetlischarged to the streams or other'boiiesof 'Water rvWill 'be 'sui'ciently pure to avoid stream Vpollutior'i"prob- Elems and ythe objection of nearby-municipalities.

Other 'features and advantages -Will appear in the fac- -fcompanyin'g drawings and the ifollowing specification wherein -Wehave illustrated and described a preferred `i`orm oif-lproee`ss-embodying lour 'inventive concept. How- 1ever,'itfis-*tobeiunderstood that "our invention is not "to be construed as limited to the specific process disclosed nor To -the particular equipment used except as determined by the scope of the appended claims. With referene'et'o the accompanying drawings,

Figure 1 is a schematic showing 'of the preferred em- 'bo-dimet ofthepresent invention,

Figure :Zfis' faisodium sulfate-ammonium sulfate-water phasefdiagramlshowing the weight percentages at 100 C.,

'must be removed from the gel catalyst by-Washin'g. Large. f

volumes of'dilute aqueous solution'sof sodium gsulf'atejy and ammonium sulfate are consequently obtained from 'such washings anditis'a principal'object of 'the present 'and Figure is Aa #sodium Vsulfate-ammonium sulfate-water y' Iphase .diagramjshowing the weight percentages at 15 C.

`invention to .utilize `these wash waters as advantageously as possible `under the particular circumstances.

r4inirnany cases fthe economics of -the-situationfhave ibeen 2such Ythat the vvvash'waters 'were merely run toWas'tento v--the nearest 'stream -or other body fotwater. iHoWever,

such tactics Shave become more and more inadvis'ble,

'fin th'eienibcdiment of the invention shown in the rdrawings, ithe'dilute'aiqueous filtrate It? coming from the ilters .for lother :separation equipment used in the production of .the .silicaba'lurnina gels contains the ammonium sulfate -an-d :sodium fsulfate Vin varyingproportions vdepending on -many vfactors. One particular sample-'of a Jltratef-Was analyzedand was `found kto contain a'nuammoniumrsulf' -lfatewodiurn sulfate Weight ratio of approximately 11,1.'36

lpr'incipalobject of Ithe presentinvention to provide irnproved methods of recovering such sulfatesltovoiil runningthern to Y'vvasteand to alleviate 'the'st'ream pollution problems.

Additionally, VVVthese sulfates, although not relativelyiertipensive, fdo possess commercial value and it .is j'la Astill further principal object ofthe present'invention' toprovicie frnethods of recovering suchsulfates `whereby tl'ie v"facturefo'f v'suchfcatalysts is made more' Ae'cie'ntia'nifeconomical on an overall economic basis.

We have found that these objects, as well asothe'r objects Lwhich l'will appear hereinafter, may be vobtained by concentrating'the dilute aqueous Wash'water ltrates at relatively elevated Vtemperatures to a point "sucie'nt'lt'o lcrystallize out of solution a portion of the 'sodium sul- Atate butinsufeient to crystallize any ammonium-sulfate out of solution. This crystallized sodium sulfate vmay then "be recovered in relatively pure form. Theremaining solutioniwhich vnow contains a higher ratio 'tiff-ainiinoni'um sulfate to sodium sulfate than originally-present `i'nayube cooled to a low enough temperature and concenftrate'dunder Avacuumwhereby a miXture'of-a doublef s`alt `rernoval'of the crystallized sodium sulfate. Theremain-` ing sbluton v'which 'new possesses fan even higher ratio #of ammonium Ssulfate to Vsodium sulfate-is then-heated and yconcentrated at relatively Aelevated temperatures.

Such an opertaion, however, due to the change; ofipro iportionsof the constituents, vnow results infacrystalliza- `and this :particular fratio will be employed V to describe .more lspeciiically'th'e details of the ,present invention. It Lis' tobejpointed out, however, thatsucha value hasfbeen selected merely `as villustrative of theinventive fconcept and lis 'not 'to be construed as vlimitative thereof, inas- 'much as veryfmany other ratios 4are'rpossible, Vdepending upon the yspecific operating conditions.

Theltrate is received `from such la .catalyst manufacturling. process rand analyzed '1.34 tons of ammonium .sulfate tand :lL-SZtons of sodium sulfate 1 1.36ratio) inapproXimately 150 `tonsfof'waterper hour. The ltrat'eisspass'ed through any :type -of concenration equipment, such '-as ra lthermocompressionevaporator or, as .shownin Figure .1, multi-eiect evaporators i2, 14, 16, 18, which maybe `operated -at temperatures respectively -ofapproximately 51 ,C 66 C.; 82 `C.;andfl00 C. and at-correspond- Gingly decreased pressures.

V--Duringfsuch a concentration, the sodium sulfate, --being `1in-greater concentration than theammoniumsulfate and, additionally, having a considerablylowerisolubility in water, crystallizes out first, lprior'to any crystallization". of

the ammonium sulfate. Such crystallization follows and =is :governed by -the three component sodium sulfate- -ammonium sulfate-Water phase diagram at C. shown -`in Figurel. Crystallization of the sodium sulfatestarts at `intersection point A and continues inthe direction `of intersection point B. However, the control lover 1 the evaporators is such that-the concentration of the solution yis `stopped just .prior to reaching vintersection p'oint .5B wherebyfonly sodium sulfate crystallizes out andvvsub- ,-stantially no ammonium sulfate is crystallized.

The-crystallized sodium sulfate slurry may, if desired, -be passedthrough a salt classifier 2t) which rpermits the atented Mar. 20V 1956 rators to permit their build-up into desirable large size crystals. The large-size crystals passing through the classifier may be pumped through a settler 22 and a continuously-operated centrifuge 24 whereby the sodium sulfate is separated and then passed onwardly to a drier, such as a gas-tired rotary type 26, wherein the crystals are dried prior to being placed in a storage bin 28.

A small amount of wash water may be employed to wash the sodium sulfate crystals and this wash may then be recycled back to the evaporators, as shown in Figure 1. This is represented in the table, which will be described more fully hereinafter, as wash No. 1.

The mother liquor from which the sodium sulfate crystals have been removed then goes to a receiving tank 30 wherein the sodium sulfatezammonium sulfate weight ratio is found to be approximately l to 2.5, due to the decrease in the amount of sodium sulfate. The mother liquor is then pumped to a vacuum crystallizer 32 equipped with a booster, if necessary, wherein it is cooled uto a low enough temperature and concentrated under vacuum to remove most of the remaining sodium sulfate sulfate. The evaporation is so controlled that it is continued up to a point just short of intersection point B, whereat sodium sulfate would also start precipitating out, and consequently only relatively pure ammonium sulfate is obtained at this point.

It is, of course, apparent that this concentration is not necessarily carried out at atmospheric pressure but that pressures less than atmospheric may be used with correspondingly decreased temperatures and that pressures above atmospheric may be used with correspondingly increased pressures. p

A continuous centrifuge 42 separates the crystallized ammonium sulfate and delivers the same to storage bins 44, after drying or other processing. The mother liquor may be delivered to a receiving tank 46 and then may be recycled, for example, to be mixed with the mother liquor leaving tank 30.

The following table sets forth the Weights of materials per hour processed, the percentage compositions thereof and the approximate temperatures at the various stages of the operation.

Table Tons Per Hour Composition, Percent Materna Tnp" NaSO (N H4) QSO; H10 NaiSOi (N H0250;

Dilute Filtrate 1. 82 1. 34 150 1. 10 0. 88 29 Saturated Liquor-. 1. 82 1. 34 4. 14 25.0 .0 72 NagSOr lurry 3. 52 2.16 2. 21 34% Crystals 85-100 Mother Liquor-Tank 0. 85 2. 16 2. 21 16. 5 .1 100 M. L. Vac. Cryst. 32- 1.20 3. 04 3.13 16.5 41. 1 100 Mixed Salt Slurry 0. 85 0. 82 0. 10 48 46. 3 15 Mother Liquor Tank 0.35 2. 22 3.16 6.2 39.4 15 Mother Liquor Tank 46 0.35 0. 88 0. 92 16. 5 41. 1 100 Mixed Salt Tank 36-.-. 0. 85 0.82 1. 7 25. 0 24.0 90-100 Wash 1 0.85 1. 8 32. 0 72 Na1SO4 to Storage-.-.- 1.82 100 (NHgSOi to Storage l. 34 100 byprecipitating out quantities of the double saltof sodium sulfate and ammonium sulfate. The crystallization follows and is governed by the three component sodium sulfate-ammonium sulfate-water phase diagram 4 shown in Figure 3 which, primarily for illustrative purposes, has been taken at 15 C. It is to be realized, however, that other temperatures are possible, provided the double salt crystallizes out of solution at that temperature and pressure for the particular concentration of sulfates present. For the purpose of this invention, it has been found that a temperature range of from about 0 C. to about 25 C. defines the commercially operable field.

The composition of the double salt has been found Vto be approximately 48% ammonium sulfate by weight and 52% sodium sulfate and it is to be appreciated that the removal of such a salt from the solution will ultimately result in a much higher proportion of ammonium sulfate therein.

A continuous centrifuge 34 may be employed to separate the double salt which is then delivered to a receiving tank 36 equipped with heating means (not shown) and heated prior to being recycled to the quadruple eiect evaporatorsA to be added to the dilute aqueous filtrate 10 undergoing concentration therein, whereby the percentage of the sodium and ammonium sulfates therein is increased considerably.

"Ihe mother liquor from which the mixed salts have been removed and which now possesses an even higher ammonium sulfatezsodium sulfate weight ratio, on the order of approximately 6.121, may be delivered to a receiving tank 38 and pumped to a third evaporating stage which may take the form of an atmospheric evaporator 40. This evaporation takes place at atmospheric pressure and at approximately 105 and consequently the phase diagram of Figure 2 is again controlling with the governing ratio of ammonium sulfate to sodium sulfate being about 6.1:1, Reference to Figure 2 reveals that ammonium sulfate will be precipitated out initially (note intersection point D) prior to any separation of sodium These values are, of course, merely typical of one particular installation used to recover the ammonium and sodium sulfates from a specific silica-alumina catalyst manufacturing operation. The principles of the present invention are naturally applicable to dilute aqueous wash water wastes from other sources and of other concentrations. The dilute aqueous liquor may enter the process at other initial temperatures and it is apparent that other temperature and pressure ranges for the evaporation steps are capable of use.

While we have shown and described what we believe to be a preferred embodiment of our invention in the matter of simplicity, equipment, ease of operation, etc., it will be obvious that the details of such an embodiment may be more or less modified within the scope of the appended claims Without departures from the principle involved or material sacrifice of the advantages of the preferred concept.

We claim:

l. Av method of recovering sodium sulfate and ammonium sulfate from a dilute aqueous solution containing the same which comprises concentrating said dilute aqueous solution at elevated temperatures and adjusting the sodium sulfate-ammonium sulfate ratio thereof to a point where a portion of the sodium sulfate will crystallize out A of solution at 100 C. without crystallizing out any of the ammonium sulfate and separating the crystallized sodium sulfate from its mother liquor; cooling said mother liquor to a temperature of from about 0 C. to about 25 C. whereby a double salt of sodium sulfate and ammonium sulfate crystallizes out of solution; separating said double salt from its mother liquor; concentrating -the last-mentionedmother liquor at elevated temperanium sulfate from a dilute aqueous solution containing the same which comprises concentrating said dilute aqueous solution at elevated temperatures and adjusting the sodium sulfate-ammonium sulfate ratio thereof to a point where a portion of the sodium sulfate will crystallize out of solution at 100 C. without crystallizing out any of the ammonium sulfate and separating the crystallized sodium sulfate from its mother liquor; cooling said mother liquor to a temperature of from about 0 C. to about 25 C. whereby a double salt of sodium sulfate and ammonium sulfate crystallizes out of solution; separating said double salt from its mother liquor and recycling the same to the dilute aqueous solution undergoing concentration; concentrating the last-mentioned mother liquor at elevated temperatures to crystallize a portion of the ammonium sulfate out of the solution but not enough to crystallize any sodium sulfate out of solution; separating the crystallized ammonium sulfate from its mother liquor; and recycling the last-mentioned mother liquor to the solution being cooled to separate the double salt.

3. A method of recovering sodium sulfate and ammonium sulfate from dilute aqueous wash water used in washing silica-alumina gels which comprises concentrating said wash water at elevated temperatures of from about 51 C. to about 100 C. and adjusting the sodium sulfate-ammonium sulfate ratio thereof to a point where a portion of the sodium sulfate will crystallize out of solution at 100 C. without crystallizing out any of the ammonium sulfate and separating the crystallized so dium sulfate from its mother liquor; cooling said mother liquor under vacua to a temperature of about 15 C. and concentrating the same whereby a double salt of sodium tion; separating said double salt from its mother liquor; concentrating the last-mentioned mother liquor at elevated temperatures to a point sufficient to crystallize a portion of the ammonium sulfate out of the solution but not enough to crystallize any sodium sulfate out of solution; and separating the crystallized ammoniumsulfate from its mother liquor.

4. A method of recovering sodium sulfate and ammonium sulfate from dilute aqueous Wash water used in washing silica-alumina gels which comprises concentrating said wash waters at elevated temperatures of from about 51 C. to about 100 C. and adjusting the sodium sulfate-ammonium sulfate ratio thereof to a point where a portion of the sodium sulfate will crystallize out of solution at C. Without crystallizing out any of the ammonium sulfate and separating the crystallized sodium sulfate from its mother liquor; cooling said mother liquor to a temperature of about 15 C. and concentrating the same whereby a double salt of sodium sulfate and ammonium sulfate crystallizes out of solution; separating said double salt from its mother liquor and recycling the same to the wash water undergoing concentration; concentrating the last-mentioned mother liquor double salt at elevated temperatures to a point suflicient to crystallize a portion of the ammonium sulfate out of the solution but not enough to crystallize any sodium sulfate out of solution; separating the crystallized ammonium sulfate from its mother liquor; and recycling the last-mentioned mother liquor to the solution being cooled to separate the double salt.

No references cited. 

4. A METHOD OF RECOVERING SODIUM SULFATE AMMONIUM SULFATE FROM DILUTE AQUEOUS WASH WATER USED IN WASHING SILICA-ALUMINA GELS WHICH COMPRISES CONCENTRATING SAID WASH WATERS AT ELEVATED TEMPERATURES OF FROM ABOUT 51* C. TO ABOUT 100* C. AND ADJUSTING THE SODIUM SULFATE-AMMONIUM SULFATE RATIO THEREOF TO A POINT WHERE A PORTION OF THE SODIUM SULFATE WILL CRYSTALLIZE OUT OF SOLUTION AT 100* C. WITHOUT CRYSTALLIZING OUT ANY OF THE AMMONIUM SULFATE AND SEPARATING THE CRYSTALLIZED SODIUM SULFATE FROM ITS MOTHER LIQUOR; COOLING SAID MOTHER LIQUOR TO A TEMPERATURE OF ABOUT 15*C. AND CONCENTRATING THE SAME WHEREBY A DOUBLE SALT OF SODIUM SULFATE AND AMMONIUM SULFATE CRYSTALLIZES OUT OF SOLUTION; SEPARATING SAID DOUBLE SALT FROM ITS MOTHER LIQUOR AND RECYCLING THE SAME TO THE WASH WATER UNDERGOING CONCENTRATION; CONCENTRATING THE LAST-MENTIONED MOTHER LIQUOR DOUBLE SALT AT ELEVATED TEMPERATURES TO A POINT SUFFICIENT TO CRYSTALLIZE A PORTION OF THE AMMONIUM SULFATE OUT OF THE SOLUTION BUT NOT ENOUGH TO CRYSTALLIZE ANY SODIUM SULFATE OUT OF SOLUTION; SEPARATING THE CRYSTALLIZED AMMONIUM SULFATE FROM ITS MOTHER LIQUOR; AND RECYCLING THE LAST-MENTIONED MOTHER LIQUOR TO THE SOLUTION BEING COOLED TO SEPARATED THE DOUBLE SALT. 